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James B. Shanley

Publications and source records attributed to James B. Shanley.

84 records · Page 5Linked to original sources
USGS2009

The stable isotope amount effect: New insights from NEXRAD echo tops, Luquillo Mountains, Puerto Rico

The stable isotope amount effect has often been invoked to explain patterns of isotopic composition of rainfall in the tropics. This paper describes a new approach, correlating the isotopic composition of precipitation with cloud height and atmospheric temperature using NEXRAD radar echo tops, which are a measure of the maximum altitude of rainfall within the clouds. The seasonal differences in echo top altitudes and their corresponding temperatures are correlated with the isotopic composition of rainfall. These results offer another factor to consider in interpretation of the seasonal variation in isotopic composition of tropical rainfall, which has previously been linked to amount or rainout effects and not to temperature effects. Rain and cloud water isotope collectors in the Luquillo Mountains in northeastern Puerto Rico were sampled monthly for three years and precipitation was analyzed for δ 18 O and δ 2 H. Precipitation enriched in 18 O and 2 H occurred during the winter dry season (approximately December–May) and was associated with a weather pattern of trade wind showers and frontal systems. During the summer rainy season (approximately June–November), precipitation was depleted in 18 O and 2 H and originated in low pressure systems and convection associated with waves embedded in the prevailing easterly airflow. Rain substantially depleted in 18 O and 2 H compared to the aforementioned weather patterns occurred during large low pressure systems. Weather analysis showed that 29% of rain input to the Luquillo Mountains was trade wind orographic rainfall, and 30% of rainfall could be attributed to easterly waves and low pressure systems. Isotopic signatures associated with these major climate patterns can be used to determine their influence on streamflow and groundwater recharge and to monitor possible effects of climate change on regional water resources.

Water Resources Research↗
USGS2009

Responses of stream nitrate and dissolved organic carbon loadings to hydrological forcing and climate change in an upland forest of the northeast USA

[1] In coming decades, higher annual temperatures, increased growing season length, and increased dormant season precipitation are expected across the northeastern United States in response to anthropogenic forcing of global climate. We synthesized long-term stream hydrochemical data from the Sleepers River Research Watershed in Vermont, United States, to explore the relationship of catchment wetness to stream nitrate and DOC loadings. We modeled changes in growing season length and precipitation patterns to simulate future climate scenarios and to assess how stream nutrient loadings respond to climate change. Model results for the 2070–2099 time period suggest that stream nutrient loadings during both the dormant and growing seasons will respond to climate change. During a warmer climate, growing season stream fluxes (runoff +20%, nitrate +57%, and DOC +58%) increase as more precipitation (+28%) and quick flow (+39%) occur during a longer growing season (+43 days). During the dormant season, stream water and nutrient loadings decrease. Net annual stream runoff (+8%) and DOC loading (+9%) increases are commensurate with the magnitude of the average increase of net annual precipitation (+7%). Net annual stream water and DOC loadings are primarily affected by increased dormant season precipitation. In contrast, decreased annual loading of stream nitrate (−2%) reflects a larger effect of growing season controls on stream nitrate and the effects of lengthened growing seasons in a warmer climate. Our findings suggest that leaching of nitrate and DOC from catchment soils will be affected by anthropogenic climate forcing, thereby affecting the timing and magnitude of annual stream loadings in the northeastern United States.

Vermont↗
USGS2009

Selected achievements, science directions, and new opportunities for the WEBB small watershed research program

Over nearly two decades, the Water, Energy, and Biogeochemical Budgets (WEBB) small watershed research program of the U.S. Geological Survey (USGS) has documented how water and solute fluxes, nutrient, carbon, and mercury dynamics, and weathering and sediment transport respond to natural and humancaused drivers, including climate, climate change, and atmospheric deposition. Together with a continued and increasing focus on the effects of climate change, more investigations are needed that examine ecological effects (e.g., evapotranspiration, nutrient uptake) and responses (e.g., species abundances, biodiversity) that are coupled with the physical and chemical processes historically observed in the WEBB program. Greater use of remote sensing, geographic modeling, and habitat/watershed modeling tools is needed, as is closer integration with the USGS-led National Phenology Network. Better understanding of process and system response times is needed. The analysis and observation of land-use and climate change effects over time should be improved by pooling data obtained by the WEBB program during the last two decades with data obtained earlier and (or) concurrently from other research and monitoring studies conducted at or near the five WEBB watershed sites. These data can be supplemented with historical and paleo-environmental information, such as could be obtained from tree rings and lake cores. Because of the relatively pristine nature and small size of its watersheds, the WEBB program could provide process understanding and basic data to better characterize and quantify ecosystem services and to develop and apply indicators of ecosystem health. In collaboration with other Federal and State watershed research programs, the WEBB program has an opportunity to contribute to tracking the short-term dynamics and long-term evolution of ecosystem services and health indicators at a multiplicity of scales across the landscape.

Conference Paper↗
USGS2009

Using high-frequency sampling to detect effects of atmospheric pollutants on stream chemistry

We combined information from long-term (weekly over many years) and short-term (high-frequency during rainfall and snowmelt events) stream water sampling efforts to understand how atmospheric deposition affects stream chemistry. Water samples were collected at the Sleepers River Research Watershed, VT, a temperate upland forest site that receives elevated atmospheric deposition of pollutants such as nitrogen (N) and mercury (Hg). Our use of high-frequency sampling documents responses of nutrients and mercury in streamflow to atmospheric deposition inputs to the watershed.

Conference Paper↗
USGS2008

Sources, transformations, and hydrological processes that control stream nitrate and dissolved organic matter concentrations during snowmelt in an upland forest

We explored catchment processes that control stream nutrient concentrations at an upland forest in northeastern Vermont, USA, where inputs of nitrogen via atmospheric deposition are among the highest in the nation and affect ecosystem functioning. We traced sources of water, nitrate, and dissolved organic matter (DOM) using stream water samples collected at high frequency during spring snowmelt. Hydrochemistry, isotopic tracers, and end‐member mixing analyses suggested the timing, sources, and source areas from which water and nutrients entered the stream. Although stream‐dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) both originated from leaching of soluble organic matter, flushing responses between these two DOM components varied because of dynamic shifts of hydrological flow paths and sources that supply the highest concentrations of DOC and DON. High concentrations of stream water nitrate originated from atmospheric sources as well as nitrified sources from catchment soils. We detected nitrification in surficial soils during late snowmelt which affected the nitrate supply that was available to be transported to streams. However, isotopic tracers showed that the majority of nitrate in upslope surficial soil waters after the onset of snowmelt originated from atmospheric sources. A fraction of the atmospheric nitrogen was directly delivered to the stream, and this finding highlights the importance of quick flow pathways during snowmelt events. These findings indicate that interactions among sources, transformations, and hydrologic transport processes must be deciphered to understand why concentrations vary over time and over space as well as to elucidate the direct effects of human activities on nutrient dynamics in upland forest streams.

Water Resources Research↗
USGS2008

Seasonal and event variations in δ 34 S values of stream sulfate in a Vermont forested catchment: Implications for sulfur sources and cycling

Stable sulfur (S) isotope ratios can be used to identify the sources of sulfate contributing to streamwater. We collected weekly and high-flow stream samples for S isotopic analysis of sulfate through the entire water year 2003 plus the snowmelt period of 2004. The study area was the 41-ha forested W-9 catchment at Sleepers River Research Watershed, Vermont, a site known to produce sulfate from weathering of sulfide minerals in the bedrock. The δ 34 S values of streamwater sulfate followed an annual sinusoidal pattern ranging from about 6.5‰ in early spring to about 10‰ in early fall. During high-flow events, δ 34 S values typically decreased by 1 to 3‰ from the prevailing seasonal value. The isotopic evidence suggests that stream sulfate concentrations are controlled by: (1) an overall dominance of bedrock-derived sulfate ( δ 34 S ~ 6–14‰); (2) contributions of pedogenic sulfate ( δ 34 S ~ 5–6‰) during snowmelt and storms with progressively diminishing contributions during base flow recession; and (3) minor effects of dissimilatory bacterial sulfate reduction and subsequent reoxidation of sulfides. Bedrock should not be overlooked as a source of S in catchment sulfate budgets.

Vermont↗
USGS2006

Detection of water quality trends at high, median, and low flow in a Catskill Mountain stream, New York, through a new statistical method

The effects of changes in acid deposition rates resulting from the Clean Air Act Amendments of 1990 should first appear in stream waters during rainstorms and snowmelt, when the surface of the watershed is most hydrologically connected to the stream. Early detection of improved stream water quality is possible if trends at high flow could be separately determined. Trends in concentrations of sulfate (SO 4 2− ), nitrate (NO 3 − ), calcium plus magnesium (Ca 2+ +Mg 2+ ), and acid‐neutralizing capacity (ANC) in Biscuit Brook, Catskill Mountains, New York, were assessed through segmented regression analysis (SRA). The method uses annual concentration‐to‐discharge relations to predict concentrations for specific discharges, then compares those annual values to determine trends at specific discharge levels. Median‐flow trends using SRA were comparable to those predicted by the seasonal Kendall tau test and a multiple regression residual analysis. All of these methods show that stream water SO 4 2− concentrations have decreased significantly since 1983; Ca 2+ +Mg 2+ concentrations have decreased at a steady but slower rate than SO 4 2− ; and ANC shows no trend. The new SRA method, however, reveals trends that differ at specified flow levels. ANC has increased, and NO 3 − concentrations have decreased at high flows, but neither has changed as significantly at low flows. The general downward trend in SO 4 2− flattened at median flow and reversed at high flow between 1997 and 2002. The reversal of the high‐flow SO 4 2− trend is consistent with increases in SO 4 2− concentrations in both precipitation and soil solutions at Biscuit Brook. Separate calculation of high‐flow trends provides resource managers with an early detection system for assessing changes in water quality resulting from changes in acidic deposition.

Water Resources Research↗
USGS2005

Tracing sources of streamwater sulfate during snowmelt using S and O isotope ratios of sulfate and 35S activity

The biogeochemical cycling of sulfur (S) was studied during the 2000 snowmelt at Sleepers River Research Watershed in northeastern Vermont, USA using a hydrochemical and multi-isotope approach. The snowpack and 10 streams of varying size and land use were sampled for analysis of anions, dissolved organic carbon (DOC), 35 S activity, and δ 34 S and δ 18 O values of sulfate. At one of the streams, δ 18 O values of water also were measured. Apportionment of sulfur derived from atmospheric and mineral sources based on their distinct δ 34 S values was possible for 7 of the 10 streams. Although mineral S generally dominated, atmospheric-derived S contributions exceeded 50% in several of the streams at peak snowmelt and averaged 41% overall. However, most of this atmospheric sulfur was not from the melting snowpack; the direct contribution of atmospheric sulfate to streamwater sulfate was constrained by 35 S mass balance to a maximum of 7%. Rather, the main source of atmospheric sulfur in streamwater was atmospheric sulfate deposited months to years earlier that had microbially cycled through the soil organic sulfur pool. This atmospheric/pedospheric sulfate (pedogenic sulfate formed from atmospheric sulfate) source is revealed by δ 18 O values of streamwater sulfate that remained constant and significantly lower than those of atmospheric sulfate throughout the melt period, as well as streamwater 35 S ages of hundreds of days. Our results indicate that the response of streamwater sulfate to changes in atmospheric deposition will be mediated by sulfate retention in the soil.

Vermont↗
USGS2003

Shallow water table fluctuations in relation to soil penetration resistance

Hydrologic modeling of catchments is frequently hampered by lack of information on subsurface stratigraphy and zones of preferred flow. We evaluated the usefulness of soil penetration resistance, easily measured by a dynamic cone penetrometer, together with measurements of ground water level fluctuations, as a cost-effective means to infer subsurface flow patterns. At our field site at Sleepers River, Vermont, penetration resistance was lowest in the surficial 10 to 30 cm, then typically increased to a local maximum at 60 to 80 cm, which we interpreted as the soil/till interface. Below this depth usually lies a zone of decreased resistance in the till, giving way to either a gradual or abrupt increase in resistance toward the bedrock surface at 1 to 4.5 m depth. Penetration resistance had a weak but significant negative correlation with saturated hydraulic conductivity determined by bail tests (r 2 = 0.25, p < 0.05). At many wells, monthly ground water levels tended to cluster at or just above the resistant zone near the soil/till interface. Chemical and isotopic dynamics in nested wells finished above and below the resistant zone suggest that the zone may temporarily isolate the deeper ground water reservoir from meltwater inputs, which were clearly identified by low δ 18 O values. In ground water discharge zones, δ 18 O values tended to converge throughout the profile. In contrast, dissolved organic carbon (DOC) maintained a gradient of increasing concentration toward land surface, even in otherwise well-mixed waters, reflecting its rapid release from organic horizons. Understanding the effect of soil penetration resistance on ground water behavior may be useful in future catchment modeling efforts.

Vermont↗
USGS2000

Sleepers River, Vermont: a Water, Energy, and Biogeochemical Budgets Program site

The Sleepers River Research Watershed in northeastern Vermont was established by the Agricultural Research Service (ARS) of the U.S. Department of Agriculture in 1959 and is now operated jointly by the U.S. Geological Survey (USGS) and the U.S. Army Cold Regions Research and Engineering Laboratory (CRREL), will collaboration from several other Federal Agencies and Universities. The USGS has contributed to the understanding of hydrological processes and added a major biogeochemical cycling research component in the last 10 years of Sleepers River's 40-year history as a field laboratory. The USGS uses hydrologic measurements and chemical and isotopic tracing techniques to determine how water moves from the hillslope to the stream, and what processes cause chemical changes, such as neutralization of acid rain. Research results provide insights on how pollutants move through ecosystems, and how ecosystems may respond to climatic change.

Vermont↗
USGS1998

Isotopes as indicators of environmental change

In addition to providing an understanding of processes within a catchment system, isotopic techniques have been instrumental in providing reconstructions of catchment climate and other environmental indicators at various time scales. Many recent changes are a direct consequence of anthropogenic activities. Isotopic analysis serves as a valuable tool for distinguishing between natural variations in long-term climatic patterns and anthropogenic effects, yielding improved understanding of natural feedback mechanisms and the development of realistic remediation strategies. This chapter discusses the examples of isotopic techniques that have been applied to understand several types of ongoing and recent environmental changes, and in paleo-environmental studies. It discusses isotope geochemistry, hydrology, and climatology to look at new ways of applying isotopic tracing techniques to provide information on environmental change. It also gives an overview on how isotopic indicators are being applied in investigations of environmental change in continental settings.

Book chapter↗
USGS1995

Water, energy, and biogeochemical budget research at Sleepers River Research Watershed, Vermont

The U.S. Geological Survey has selected the Sleepers River Research Watershed (Sleepers River) near Danville, Vt., as one of five sites for the investigation of Water, Energy, and Biogeochemical Budgets (WEBB). Sleepers River was chosen because it is a well-designed outdoor laboratory with a long history of hydrologic data collection and research, and also because it provides an ideal opportunity for collaboration among the U.S. Geological Survey, other Federal agencies, and universities at the site. The multiple subwatersheds at Sleepers River present a unique opportunity to investigate hydrologic, energy, and biogeochemical processes over a variety of spatial scales. This WEBB study builds on fundamental research on process mechanisms and rates at the plot scale (in this case, a hillslope). Results then are scaled up to interpret the hydrochemical response of first- and higher- order basins. Five research elements make up the Sleepers River WEBB project. Individually, each of the five elements is designed to investigate specific WEBB processes (such as CO2 efflux through a snowpack), address specific WEBB issues (such as scaling and flowpaths), or apply specific WEBB approaches (such as integrated chemical and physical study of a hillslope). The research elements overlap so that many of the processes investigated will be assessed in more than one way, thus allowing independent verification of research results. For example, flowpath information will be derived separately by use of isotopic tracers, conservative chemical solutes, and soil-moisture fluxes. Collectively, the five elements constitute an integrated approach to a comprehensive understanding of WEBB processes needed for the prediction of the effects of global change.

Open-File Report↗